negative dihedral

on 6/4/2008 9:54 PM Bertie the Bunyip said the following:
Rich Ahrens wrote in news:484753e0$0$76834
:

on 6/3/2008 10:35 PM Bertie the Bunyip said the following:
I think there have been a couple of straight wing airplanes wiht
anhedral, but I can't picture one off the top of my head. Surely
everything that can be tried, has been tried at this stage!
The Lockheed F-104, perhaps?


Yep, dats one. i have no idea what the anhedral does on that, but I'm going
to take a blind stab at area rule.

The usual, I think - Dutch roll control. The vertical fin was almost as
long as the wings.

Rich Ahrens wrote in
. net:

on 6/4/2008 9:54 PM Bertie the Bunyip said the following:
Rich Ahrens wrote in news:484753e0$0$76834
:

on 6/3/2008 10:35 PM Bertie the Bunyip said the following:
I think there have been a couple of straight wing airplanes wiht
anhedral, but I can't picture one off the top of my head. Surely
everything that can be tried, has been tried at this stage!
The Lockheed F-104, perhaps?


Yep, dats one. i have no idea what the anhedral does on that, but I'm
going to take a blind stab at area rule.

The usual, I think - Dutch roll control. The vertical fin was almost
as long as the wings.


Mm. Dunno. The fin would be neccesary because of the center of pressure
change anyway. You're right though. anhedral would dampen any high
speed dutch roll tendencies by reducing the alpha on an advancing wing.,
but the rules for things like that with razor thin wings get a bit weird
anyway. Trans-sonic it shouldn't have many issues anyway since
compressibility is dealt with by the airfoil, but you're probably right.
Its a shame. I was flying with a former aeronautical engineer the other
day and could have asked him.



Bertie

On Jun 4, 2:30*pm, Tina wrote:
On Jun 3, 10:25 pm, Bertie the Bunyip wrote:



Tina wrote in news:d9fb071f-4d30-45c3-916d-
:

I understand how positive dihedral helps dynamic stability in
airplanes, but some big ones, like the Russian An 124 Condor, has a
pronounced negative dihedral -- the wings have a noticeable downward
slope.

That's called Anhedral..

Q1: Do those airplanes need active fly by wire controls to maintain
stability, or is something else at play that keeps them right side up?

Nope.

Q2: Does anyone have a design rationalization *for such a
configuration, as opposed to just zero dihedral? I can appreciate why
fighters have it -- they exploit lack of aerodynamic stability for
rapid *maneuvers -- but transports that spend their whole life being
straight and level are another issue.

Well, the anhedral negates what can be excessive stability that comes
form the sweep of the wings. Sweep provides a very similar kind of
stability as does dihedral and the addition of anhedral negates some of
this and keeps the airplane form becoming so stable that it can't even
be maneuvered!
Most of the airplanes with pronounced anhedral are high wing and would
have parasol stability as well. The anhedral helps neutralise some of
that. Some low wing Russian jets have anhedral, but it's quite small
Their sweep is quite marked and the anhedral is there to ammeliarate
that. The 727 had a fairly radical sweep and you will notice, that
though it has dihedral it's very little compared to the 737 or similar.

Note: I have not morphed into an Mx clone!

We'll know for sure if you tell me this answer is completely wrong
because your MSFS 172 doesn't have anhedral.

Bertie

Only after a very hard landing would a 172 develop negative dihedral.
A Mooney, on the other hand, given the placement of the wheels, would
either increase its positive dihedral, or more likely, given how
strongly they are built, put a dent in the runway.

With those struts I would expect polyanhedral!

Cheers